Is there a hadith establishing the permissibility of selling mothers?

Abu Malik: Is there a hadith establishing the permissibility of selling the mothers of children? I mean the female slaves.

The Shaykh : This sale of the mothers of children used to take place during the time of the Messenger (peace and blessings be upon him). However, there is guidance in some of his (peace and blessings be upon him) verbal hadiths not to separate the master from the child and his mother. Therefore, 'Umar ibn al-Khattab (may Allah be pleased with him) adopted this noble Prophetic guidance and prohibited the sale of the mothers of children. We say here that there are two matters, as the jurists express it: here is a fatwa, and here is the piety of the fatwa. As long as this matter used to take place during the time of the Messenger (peace and blessings be upon him) and he did not denounce it, it is permissible. As for the piety, it is that the Muslim does not do that, out of mercy for the child and his mother.
Abu Malik: But the sale is valid, meaning.

The Shaykh : Yes, that is what we mean by the fatwa.